AUKE BAY LABORATORY (ABL) (cont.)

Ocean Carrying Capacity Program

Distribution, Migration, and Relative Abundance of Juvenile Salmon in the Eastern Bering Sea

Scientists from the ABL Ocean Carrying Capacity (OCC) program conducted research cruises to survey juvenile Pacific salmon in the eastern Bering Sea during 2000–03. The research is part of the Bering-Aleutian Salmon International Survey (BASIS), a Bering Sea ecosystem study that includes member nations (Canada, Russian, Japan, and United States) of the North Pacific Anadromous Fish Commission (NPAFC). The BASIS study was developed to clarify the mechanisms of biological response by salmon to the conditions caused by climate change.

The goal of OCC’s BASIS research is to understand mechanisms underlying the effects of environment on the distribution, migration, and growth of juvenile salmon along the eastern Bering Sea shelf. Specific objectives of the OCC research cruises are to determine migration and distribution of juvenile salmon stocks, measure early marine growth, and determine relative abundance.

Results indicate that 1) juvenile salmon are widely distributed across the eastern Bering Sea shelf, 2) species-specific distributional patterns of juvenile salmon can exist, 3) distributional patterns are likely related to principal prey sources (e.g., age-0 pollock for juvenile sockeye (O. nerka) and chum salmon, larval and juvenile sand lance for juvenile chinook), and 4) oceanographic characteristics can influence distribution and migration pathways (e.g., juvenile salmon appear to avoid areas of intense coccolithophore blooms). Size and relative abundance of juvenile sockeye and chum salmon was greatest during 2002 and 2003. Age-1.0 juvenile sockeye salmon tended to comprise the largest component of catch during fall surveys.

By Edward Farley

Eastern Bering Sea (BASIS) Coastal Research

Scientists from OCC program conducted a research cruise in the eastern Bering Sea during August–October 2004 as part of BASIS. The cruise was to study early marine distribution, migration, and growth of juvenile Pacific salmon (Oncorhynchus spp.) and associated marine species on the eastern Bering Sea shelf.

A total of 8,970 salmon were captured, including juvenile pink (O. gorbuscha; 20.9%), chum (O. keta; 19.4%), sockeye (O. nerka; 42.6%), coho (O. kisutch; 3.9%), and chinook (O. tshawytscha; 5.3%) salmon. Less than 9% of the catch consisted of immature and mature chum, sockeye, and chinook salmon.

A total of 2,837,503 other marine fish species were captured during the survey, including age-0 walleye pollock (Theragra chalcogramma; 91.6%) and Pacific herring (Clupea pallasi; 6.9%).

The catch also included less than 1% each for crested sculpin (Blepsias bilobus), sturgeon poacher (Podothecus acipenserinus), Bering wolffish (Anarhichas orientalis), Pacific sandfish (Trichodon trichodon), capelin (Mallotus villosus), Pacific cod (Gadus macrocephalus), prowfish (Zaprora silenus), Pacific sand lance (Ammodytes hexapterus), northern rock sole (Lepidopsetta peracuata), lamprey (Petromyzontidae), sablefish (Anoplopoma fimbria), Atka mackerel (Pleurogrammus monopterygius), starry flounder (Platichthys stellatus), rainbow smelt (Osmerus mordax), rock greenling (Hexagrammos lagocephalus), salmon shark (Lamna ditropis), saffron cod (Eleginus gracilis), ninespine stickleback (Pungitus pungitus), yellowfin sole (Limanda aspera), rockfish (Sebastes spp), plain sculpin (Myoxocephalus jaok), Bering poacher (Occella dodecaedron), antlered sculpin (Enophrys diceraus), Greenland halibut (Reinhardtius hippoglossoides), snake prickleback (Lumpenus sagitta), and ribbed sculpin (Triglops pingeli).

By Ed Farley

GLOBEC Field Survey

A Global Ocean Ecosystem Dynamics (GLOBEC) cruise was conducted in October–November 2004 to investigate the relationships between physical and biological oceanographic processes that affect the distribution and biology of juvenile Pacific salmon in the Gulf of Alaska. Measurements focused on the spatial pattern of salmon distribution, oceanographic properties, and the distribution of zooplankton along selected transects. The survey included six transects beginning with the Cape Kumlik transect, located southeast of Kodiak Island and ending with the Cape Douglas transect, located northwest of Afognak Island. Transects were perpendicular to shore and extended from nearshore across the continental shelf to oceanic waters beyond the 200-m shelf break.

The survey was conducted aboard the commercial fishing vessel Great Pacific. Fish samples were collected using a 198-m long midwater rope trawl with hexagonal mesh wings and body. Salmon and other fishes were sorted by species and counted. Standard biological measurements including fork length, body weight, and sex were made. Scale samples from the preferred area (to document age and growth) were taken from juvenile and immature salmon, and a subset of juvenile salmon was frozen whole for laboratory analyses of food habits, genetic origin, and the reading of hatchery thermal marks on otoliths.

Oceanographic measurements were made at trawl stations immediately prior to each trawl haul and included temperature, salinity, oxygen concentration, photosynthetically available radiation (PAR), chlorophyll fluorescence, and optical transmittance. Plankton samples were collected using a Bongo net frame fitted with 505-µm and 330-µm mesh nets that were towed obliquely relative to the surface. A thermosalinograph, nutrient sampler, and fluorometer provided continuous measurements of near-surface temperature, salinity, nutrients, and fluorescence. Satellite-tracked drifting buoys were deployed at designated trawl stations to measure the strength and direction of the current along the continental shelf.

During the survey, 31 trawl stations were completed, and a total of 3,549 salmon were captured. Juvenile salmon were distributed along the shelf; salmon species represented in the catch were pink (63.5%), chum (28.2%), sockeye (6.9%), coho (1.4%), and chinook (<1%) salmon. Immature salmon were located on the shelf and offshore. Species of immature salmon represented in the catch were chum (<1%) and chinook (<1%) salmon. No mature salmon were caught.

By Jamal Moss

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AFSC Quarterly Research Reports Oct-Dec 2004